<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title></title>
</head>
<body>
	<script>
			
		//String() toString() 强制类型转换
		var a = 123;
		var astr = String(a);
		console.log(astr);

		console.log(a.toString());


		var stringNum = '789.123dadadad';
		var num2 =  Number(stringNum); //NaN
		console.log(num2);


		var b1 = '123'; //true
		var b3 = -123; 
		var b4 = Infinity; 



		var b5 = NaN; //false
		var b2 = 0; //false
		var b6; //undefined
		var b7 = null;
		// 非0既真
		console.log(Boolean(b7));

	</script>
	
</body>
</html>